Remmeber to configure the serial port

Restore the lost plumbing to call Widget.SetupOutput() when the
device is opened, or we will have trouble!
Set the port baud rate to 250k

Insert the Linux platform-specific code needed to set the baud
rate to 250kbaud (at least on the Raspberry Pi). Place code in a
separate static class because the Linux includes clash with those
used elsewhere.